linux-kernel - Re: [PATCH v6 12/21] x86/virt/tdx: Add placeholder to construct TDMRs to cover all TDX memory regions

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Message-ID: <38f7e6d1c56c75dff286cf80acdd15b4869be2fd.camel@intel.com>
Date:   Thu, 3 Nov 2022 22:07:48 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>
CC:     "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v6 12/21] x86/virt/tdx: Add placeholder to construct TDMRs
 to cover all TDX memory regions

On Thu, 2022-11-03 at 08:05 -0700, Hansen, Dave wrote:
> Plus, max_reserved_per_tdmr is barely in double digits today.  It's a
> *LOOOOOOOOONG* way from either of those limits.  If you want to add a
> warning here, then go for it and enforce a sane value on
> max_reserved_per_tdmr.

Hi Dave,

Thanks. By "enforce a sane value on max_reserved_per_tdmr' could you be more
specific? Did you mean if we find its value is insanely big, we can change it to
a reasonable smaller value?

But I don't think we can as the TDMR_INFO is used by the TDX module, so reducing
max_reserved_per_tdmr by the kernel doesn't actually work?

Perhaps for now we can make the kernel to assume TDMR_INFO won't exceed a
reasonable value (i.e. 4K/8K/16K?) and max_tdmrs (which is 64 currently) won't
exceed a reasonable value either (i.e. 1K/512/256?), so that we can just use
alloc_pages_exact() to allocate  the entire TDMR array? If kernel found either
is too big, then kernel could just fail to initialize the TDX module.